Patent Document 1 discloses a touch panel which detects a touch position and a push amount by using a piezoelectric film. Polylactic acid (PLLA) stretched in a uniaxial direction is used for the piezoelectric film of the touch panel disclosed in Patent Document 1. When this PLLA is pressed, the PLLA is distorted in a normal direction of a plane. This distortion applies a force of contracting or stretching the PLLA in a direction of 45 degrees with respect to a stretching direction, and produces negative and positive charges. Further, by detecting a signal based on a potential difference between produced charge amounts, a pressing force with respect to the PLLA is detected.
Patent Document 1: International Publication No. 2013/021835 Pamphlet.